This invention relates to an induction system for an engine, and more particularly to an improved induction system for generating turbulence in the combustion chamber of the engine under at least some running conditions.
As is well known, the induction system of an engine is extremely important in determining the performance of the engine. Induction systems that provide good low-speed torque and running frequently do not produce high power outputs at wide open throttle. The reason for this is that the induction system is designed so as to generate turbulence in the combustion chamber. However, the systems in the intake passage which generate turbulence generally provide a flow restriction, and hence maximum power output cannot be achieved.
It has been proposed, therefore, to provide an induction system for an engine that employs two intake passages, one to improve the low-speed performance by introducing turbulence and the other which directs the charge into the combustion chamber in a generally axial direction with low flow restriction to achieve maximum power output. These systems are very effective in improving the engine performance throughout the entire engine load and speed ranges.
Various forms of turbulence can be induced in the intake charge. Most conventionally, a swirl is imparted to the intake air that causes the air to flow in a circular path around the cylinder bore axis. This type of turbulence is relatively easy to generate, but does not always provide optimum performance. One reason for this is that the swirl tends to dissipate during the compressive stroke of the piston and may be at its lowest when the piston is at top dead center and when combustion occurs. This is, however, the time when maximum turbulence is desired.
Another form of turbulence, which has greater effect with many types of engines is called "tumble." Tumble is also a swirling motion, but it is generated about a transverse axis. The advantage of tumble is that the rate of swirl or tumble increases as the piston approaches top dead center, and hence is at its maximum at the time of ignition. Tumble is, however, more difficult to achieve.
It is, therefore, a principal object of this invention to provide an improved induction system for an engine that employs a tumble motion under at least some running conditions.
It is a further object of this invention to provide an improved intake passage configuration wherein tumble can be easily generated and with a minimum of flow restriction.
It has also been found that certain engines benefit if the motion generated in the combustion chamber under at least the low and mid-range speed conditions is a combination of swirl and tumble. It is, therefore, a still further object of this invention to provide an improved intake passage configuration wherein swirl and tumble can be generated.
Normally, engines having plural intake ports have the intake ports all disposed on one side of a plane containing the cylinder bore axis. In order to generate a tumble motion, it is generally necessary to direct the charge so that it flows from the intake ports across the cylinder bore toward the opposite side of the plane on which the intake ports lie. With conventional valve and port construction, it is difficult to achieve this result.
It is, therefore, a still further object of this invention to provide an improved arrangement for forming a valve seat and masking the intake valve so as to achieve a tumble motion in the combustion chamber.